The present invention relates to a seat belt apparatus to be installed in a vehicle.
Conventionally, seat belt apparatuses of various forms for restraining a vehicle occupant are known for vehicles such as automobiles. In such a seat belt apparatus, it is required to increase tension on a seat belt (webbing) before and/or during a vehicle collision. Specifically, it is required to increase tension on the seat belt in order to inform a vehicle occupant of danger when a vehicle collision is predicted before the vehicle collision. Further, it is required to increase tension on the seat belt in order to improve occupant restraint when a vehicle collision is unavoidable before the vehicle collision. Furthermore, it is required to increase tension on the seat belt in order to improve occupant restraint during the vehicle collision.
For example, Japanese Unexamined Patent Publication No. H6-286581 (“JP Pub. No. '581”), which is incorporated by reference herein in its entirety, discloses a seat belt apparatus capable of increasing tension on a seat belt before and/or during a vehicle collision. In the technology described in JP Pub. No. '581, a first tension is developed on the seat belt before the vehicle collision by a reversible mechanism such as an electric motor which is disposed on a buckle side, while a second tension is developed on the seat belt during the vehicle collision by a non-reversible mechanism such as pyrotechnics, which is disposed on a retractor side.
In the seat belt apparatus as described in JP Pub. No. '581, the first mechanism for increasing the seat belt tension before a vehicle collision is disposed on the buckle side and the second mechanism for increasing the seat belt tension during the vehicle collision is disposed on the retractor side. In addition, since the first and second mechanisms are composed of different mechanisms, there is a limit to achieve reduction of the apparatus size and weight and reduction of the apparatus cost.